1. Field of the Invention
The present invention relates, in general, to a system and method for filling hydrodynamic bearings with fluid and, more particularly, to a system and method for filling hydrodynamic bearings with fluid, which can be used to fill the hydrodynamic bearings with fluid without requiring the use of a pumping unit.
2. Description of the Related Art
Generally, hydrodynamic bearings are devices used in motors of Hard Disk Drives or CD-Drives. The hydrodynamic bearing includes a shaft and a sleeve to support the shaft, with a micro-gap defined between the shaft and the sleeve and filled with viscous fluid, such as oil, thus permitting free rotation of the shaft due to dynamic pressure formed in the micro-gap caused by the fluid during relative rotation of the shaft and the sleeve.
During a process of filling the hydrodynamic bearing with fluid, it is necessary to prevent the formation of air bubbles in the micro-gap between the shaft and the sleeve. However, it is very difficult to prevent the formation of air bubbles in the micro-gap during the process of filling the bearing with fluid, and a complicated procedure is required.
A conventional fluid filling method is disclosed in Japanese Patent Laid-open Publication No. 2005-114051, entitled Method for Manufacturing Hydrodynamic Bearings and Motor using the Hydrodynamic Bearings, and is schematically shown in FIG. 4 of the accompanying drawings.
As shown in FIG. 4, a conventional system for filling hydrodynamic bearings 10 with oil comprises an oil tank 210, an air bubble removing means H and S, a vacuum vessel 220 and a needle valve 230.
The oil tank 210 stores oil with which a hydrodynamic bearing 10 is to be filled. The oil tank 210 is connected to a vacuum pump P1 through a pipe having a valve B1, and is connected through a pipe 212 to the needle valve 230 placed in the vacuum vessel 220.
The vacuum pump P1 exhausts air from the interior of the oil tank 210 to the atmosphere until the pressure in the oil tank 210 is reduced to a predetermined vacuum level P1.
The air bubble removing means H and S removes air bubbles from oil stored in the oil tank 210 and comprises a heating unit H and a stirring unit S.
The heating unit H is placed beneath the oil tank 210 and heats the oil to a predetermined temperature, thus removing air bubbles from the oil. The stirring unit S is installed in the oil tank 210 such that the unit S is immersed in the oil inside the oil tank 210. The stirring unit S stirs the oil in the oil tank 210, thus removing air bubbles from the oil.
The vacuum vessel 220 receives the hydrodynamic bearing 10 therein, and is connected to a vacuum pump P2 through a pipe having a valve B2, and communicates with the atmosphere through another pipe having a valve B3.
The vacuum pump P2 exhausts air from the interior of the vacuum vessel 220 until the pressure in the vacuum vessel 220 is reduced to a predetermined vacuum level P2. In the above state, the pressure in the vacuum vessel 220 is reduced such that the vacuum level P2 is lower than the vacuum level P1 of the oil tank 210. Described in detail, the pressure in the oil tank 210 is higher than that in the vacuum vessel 220.
The valve B3 opens the pipe to supply atmospheric air to the vacuum vessel 220, thus the pressure in the vacuum vessel 220 becomes equal to atmospheric pressure.
The needle valve 230, which drips oil onto the hydrodynamic bearing 10, is connected to the oil tank 210 through the pipe 212. The outlet nozzle of the needle valve 230 is located at a position around a tapered seal part 8 of the hydrodynamic bearing 10, thus easily dripping the fluid onto the hydrodynamic bearing 10.
The conventional system for filling hydrodynamic bearings 10 with oil, which has the above-mentioned construction, fills a hydrodynamic bearing 10 with oil while removing air bubbles from the oil, as will be described herein below.
First, the conventional oil filling system removes air bubbles from oil stored in the oil tank 210. The oil stored in the oil tank 210 under atmospheric pressure is heated by the heating unit H and is stirred by the rotating stirring unit S, and thus air bubbles are removed from the oil. At the same time, the pressure in the oil tank 210 is reduced by the vacuum pump P1 to the predetermined vacuum level P1 and is maintained at that vacuum level P1.
Thereafter, the hydrodynamic bearing 10 is received in the vacuum vessel 220, and the pressure in the vacuum vessel 220 is reduced by the vacuum pump P2 to the predetermined vacuum level P2. In the above state, air which remains in the tapered seal part 8 between the shaft and the sleeve of the hydrodynamic bearing 10 is removed in the form of air bubbles. The interior of the tapered seal part 8 is maintained at the vacuum level P2.
Thereafter, oil is dripped onto the tapered seal part 8 of the hydrodynamic bearing 10 due to the difference between the vacuum levels P1 and P2 (P1>P2).
After dripping the oil, the valve B3 is opened to introduce atmospheric air into the vacuum vessel 220, thus gradually returning the internal pressure of the vacuum vessel 220 to atmospheric pressure. In the above state, oil is pressurized by the atmospheric air flowing into the vacuum vessel 220 and is forced into all of the corners of the tapered seal part 8, thus filling the entire tapered seal part 8.
However, the conventional oil filling system and method is problematic in that, in order to drip oil onto the hydrodynamic bearing 10, the respective vacuum levels of the oil tank 210 and the vacuum vessel 220, which are reduced to create an almost perfect vacuum, must be controlled and maintained carefully such that the pressure difference between the oil tank 210 and the vacuum vessel 220 is precisely controlled.
Furthermore, to remove air bubbles from oil stored in the oil tank 210, the conventional system and method requires additional devices, such as the heating unit H and the stirring unit S, thereby complicating the construction of the system.